Charged particle beam apparatuses have many functions in a plurality of industrial fields, including, but not limited to, inspection of semiconductor devices during manufacturing, exposure systems for lithography, detecting devices and testing systems. Thus, there is a high demand for structuring and inspecting specimens within the micrometer and nanometer scale.
Micrometer and nanometer scale process control, inspection or structuring, is often done with charged particle beams, e.g. electron beams, which are generated and focused in charged particle beam devices, such as electron microscopes or electron beam pattern generators. Charged particle beams offer superior spatial resolution compared to, e.g. photon beams due to their short wavelengths.
Besides resolution, throughput is an issue with such devices. Since large substrate areas have to be patterned or inspected, throughput of, for example, larger than 10 cm2/min is desirable. In charged particle beam devices, the throughput depends quadratically on the image contrast. Thus, there is a need for contrast enhancement.
Particle detectors, e.g. electron detectors, for particle beam systems, e.g. electron microscopes, can be used for electron beam inspection (EBI), defect review (DR) or critical dimension (CD) measurement, focused ion beam systems (FIB) or the like. Upon irradiation of a sample by a primary beam of electrons, secondary particles, e.g. secondary electrons (SE), are created, which carry information about the topography of the sample, its chemical constituents, its electrostatic potential and others. In a simple detector, all of the SE are collected and guided to a sensor. An image is created where the gray level is proportional to the number of electrons collected.
High resolution electron optics systems may benefit from a short working distance between the objective lens and the sample. Secondary electron collection is therefore typically done inside the column above the objective lens. A configuration commonly found in prior-art electron-beam imaging systems is shown schematically in FIG. 1. A column with length 104, including a beam emitter 105, an objective lens 10 and a detector 115 are spaced at a working distance 120 from a sample 125. The detector 115 shown in FIG. 1 is an annular secondary-electron detector. Primary charged particle beam 130 emitted from beam emitter 105 is directed at sample 125 through an opening 135 in detector 115. A secondary charged particle beam 140, e.g. a secondary electron beam, is emitted from sample 125 in a broad cone surrounding primary charged particle beam 130. Some of the secondary electrons are collected by detector 115 to produce a secondary-electron (SE) signal 145.
Moreover, it is desired for many applications that the imaging information is increased while high-speed detection is provided. For example, upon irradiation of a sample by a primary beam of electrons, secondary electrons (SE) are created which carry information about the topography of the sample, its chemical constituents, its electrostatic potential and others. High speed detection provided with topography information and/or information on the energy of the secondary particles is a challenging task, for which continuous improvement is desired. Accordingly, improvements of the detection in the SEM-based tools, particularly in high throughput defect inspection or review tools are desired. Additionally or alternatively, separation of several signal beam bundles, e.g. with reduced cross-talk, is desired for the topography detection mode where topography information is imaged.
Further, a charged particle beam device may be operated with operating parameters, such as working distance, strength of the magnetic field of the objective lens etc., varying in certain ranges, called the operating window hereinafter. It is desirable that good images can be obtained throughout this operating window, in particular in connection with the topography detection mode.